393 resultados para Fe3
Resumo:
A formao de P no-lbil a partir de formas lbeis, adsorvidas aos oxihidrxidos de Fe e Al, razo para o baixo efeito residual da fertilizao fosfatada em solos tropicais. A reversibilidade do P no-lbil para formas lbeis nesses solos pode ser favorecida pela reduo do Fe3+ e, ou, pela diminuio da atividade dos oxihidrxidos de Fe e Al. Neste trabalho, objetivou-se avaliar a adsoro e dessoro de P, sua transformao em no-lbil e reversibilidade dessa forma em amostras de solos submetidas reduo microbiana ou qumica. Para isso, amostras de 11 solos foram homogeneizadas com 300 mg kg-1 de P na forma de NaH2PO4 em soluo, incubadas por 30 dias e, ento, submetidas a dez extraes sucessivas de P com resina de troca aninica (RTA) (tratamento sem reduo). Em seguida, outras amostras dos solos foram submetidas ambiente redutor em soluo de sacarose 0,1 mol L-1 com posterior aplicao da doses de P (300 mg kg-1) e as dez extraes sucessivas de P (tratamento reduo microbiana). Depois, outras amostras foram reduzidas/complexadas com oxalato de amnio (Ox) ou com citrato-ditionito-bicarbonato (CDB), e os solos/resduos receberam a mesma dose de P dos experimentos anteriores. Foram ento incubados por 30 dias e submetidos s extraes sucessivas com RTA (tratamento reduo qumica). A capacidade mxima de adsoro de P (CMAP) dos solos mostrou-se mais dependente da goethita (com 70,8 % de contribuio para seu valor) do que da gibbsita (com contribuio de 29,2 %). A correlao negativa entre os teores de P obtidos na segunda extrao com a RTA, nos solos em condio natural, sem reduo, e os teores de gibbsita sugere que este, e no a goethita, o oxihidrxido responsvel pela maior restrio dessoro do P. Os valores de CMAP, estimados por meio do P remanescente (P-rem), mostraram, nas amostras submetidas ao tratamento com reduo microbiana, pequena alterao para o grupo dos solos menos oxdicos, com menor CMAP. Todavia, nos solos mais oxdicos, com maior CMAP, o efeito prvio da sacarose foi o aumenta do P-rem (diminuio da CMAP) 10 vezes em relao aos solos para o tratamento sem reduo. Entretanto, a reduo gerada pela sacarose no alterou a dessoro do P anteriormente adsorvido. A expectativa de que ocorreria significativa reversibilidade de P no-lbil com a reduo microbiana ou qumica dos solos no se concretizou, demonstrando a grande estabilidade dessas formas.
Resumo:
Solos de vrzea sob cultivo de arroz irrigado contribuem com aproximadamente 18 % das emisses totais de metano (CH4) do Estado do Rio Grande do Sul. Entretanto, a liberao de CH4 depende do curso de reduo de cada solo. O objetivo do presente estudo foi avaliar a dinmica da emisso desse gs de efeito estufa (GEE) em seis solos: Gleissolo (2), Planossolo (2), Chernossolo e Neossolo, representativos do cultivo de arroz irrigado no Sul do Brasil, visando identificar tambm sua relao com propriedades do solo e as alteraes eletroqumicas da soluo aps o alagamento. O experimento foi realizado em casa de vegetao, com trs repeties, segundo delineamento de blocos casualizados. Os solos foram dispostos em vasos de PVC mantidos com uma lmina de gua de 10 cm de altura e cultivados com arroz. A avaliao das emisses de CH4 foi realizada semanalmente, do 3 ao 66 dia aps o alagamento (DAA) do solo, com o auxlio de uma cmara de PVC acoplada ao topo dos vasos. As amostras de ar foram coletadas em quatro intervalos de 5 min, para estimativa das taxas de emisso de CH4. A soluo do solo tambm foi coletada e caracterizada. O incio da emisso de CH4 variou entre os solos e, normalmente, ocorreu aps a quase total reduo do Fe3+ (em torno de 90 % da maior liberao de Fe2+) e estabilizao dos valores de pH e de Eh da soluo. A emisso total de CH4 variou de 8,5 a 44,2 g m-2 e apresentou relao sigmoidal com os teores de C orgnico dos solos (r=0,83, p < 0,05), sugerindo que a disponibilidade de C somente foi limitante para o processo de metanognese em teores inferiores a 8 g kg-1 de C no solo. Os resultados mostram que a dinmica e as quantidades totais de CH4 emitidas so influenciadas pelo tipo de solo e que esforos devem ser direcionados para determinao dos fatores de emisso de CH4 para os diferentes solos representativos da produo de arroz no Sul do Brasil, bem como na avaliao do efeito de prticas agrcolas na mitigao das emisses desse GEE nos diferentes solos.
Resumo:
In addition to the more reactive forms, metals can occur in the structure of minerals, and the sum of all these forms defines their total contents in different soil fractions. The isomorphic substitution of heavy metals for example alters the dimensions of the unit cell and mineral size. This study proposed a method of chemical fractionation of heavy metals, using more powerful extraction methods, to remove the organic and different mineral phases completely. Soil samples were taken from eight soil profiles (0-10, 10-20 and 20-40 cm) in a Pb mining and metallurgy area in Adrianpolis, Paran, Brazil. The Pb and Zn concentrations were determined in the following fractions (complete phase removal in each sequential extraction): exchangeable; carbonates; organic matter; amorphous and crystalline Fe oxides; Al oxide, amorphous aluminosilicates and kaolinite; and residual fractions. The complete removal of organic matter and mineral phases in sequential extractions resulted in low participation of residual forms of Pb and Zn in the total concentrations of these metals in the soils: there was lower association of metals with primary and 2:1 minerals and refractory oxides. The powerful methods used here allow an identification of the complete metal-mineral associations, such as the occurrence of Pb and Zn in the structure of the minerals. The higher incidence of Zn than Pb in the structure of Fe oxides, due to isomorphic substitution, was attributed to a smaller difference between the ionic radius of Zn2+ and Fe3+.
Resumo:
Synthetic aluminum-substituted maghemites were characterized by total chemical analysis, powder X-ray diffraction (XRD), Mssbauer spectroscopy (ME), and vibrating sample magnetometry (VSM). The aim was to determine the structural, magnetic, and hyperfine properties of γ-Fe2-xAl xO3 as the Al concentration is varied. The XRD results of the synthetic products were indexed exclusively as maghemite. Increasing Al for Fe substitution decreased the mean crystalline dimension and shifted all diffraction peaks to higher 2θ angles. The a0 dimension of the cubic unit cell decreased with increasing Al according to the equation a o = 0.8385 - 3.63 x 10-5 Al (R= 0.94). Most Mssbauer spectra were composed of one sextet, but at the highest substitution rate of 142.5 mmol mol-1 Al, both a doublet and sextet were obtained at 300 K. All hyperfine parameters from the sub-spectra were consistent with high-spin Fe3+ (0.2 a 0.7 mms-1) and suggested a strong superparamagnetic component associated with the doublet. The magnetic hyperfine field of the sextets decreased with the amount of Al-substitution [Bhf (T) = 49.751 - 0.1202Al; R = 0.94] while the linewidth increased linearly. The saturation magnetization also decreased with increasing isomorphous substitution.
Resumo:
Localizado na poro centro-oeste do Estado de Minas Gerais, o Quadriltero Ferrfero abrange uma rea de aproximadamente 7.000 km. Desde o sculo XVII, a regio conhecida como uma provncia aurfera e ferrfera, sendo por essa razo uma das regies mais bem estudadas do Brasil no contexto geolgico. A regio de topografia muito acidentada, onde predominam solos pouco evoludos pedogeneticamente, com destaque para Cambissolos Hplicos, Neossolos Litlicos e Neossolos Regolticos. Em menor proporo e em rampas de colvio (relevo suave ondulado), ocorrem Latossolos Vermelhos muito ricos em Fe, anteriormente denominados Latossolos Ferrferos. Neste trabalho, foram realizados estudos para caracterizar fsica, qumica e mineralogicamente amostras de nove perfis de Latossolos Vermelhos frricos e perfrricos, desenvolvidos de itabirito e rochas afins no Quadriltero Ferrfero, com os objetivos de melhor entender sua gnese e avaliar critrios taxonmicos que permitam sua diferenciao no SiBCS, em nveis categricos mais baixos. Os elevados valores de densidade de partculas so peculiares nesses solos e, ao lado da estrutura forte, muito pequena e granular, so fatores que contribuem para subestimar os teores de argila e superestimar os de silte, resultando em relao silte/argila maior do que aquela proposta pelo SiBCS para os Latossolos. A variao dos teores de SiO2, Fe2O3, Al2O3, TiO2, MnO, P2O5 e de alguns elementos-trao aponta para a diversidade na composio qumica do itabirito ou, ainda, provvel mistura com rochas filticas da regio. Os valores das relaes Fe2O3/TiO2 (no molecular) e TiO2/Fe2O3 (molecular) revelaram-se diferentes daqueles sugeridos na literatura para separao de Latossolos Vermelhos desenvolvidos de itabirito daqueles de rochas mficas. As fraes areia, silte e argila apresentaram grande variao na atrao magntica, com as duas primeiras fraes evidenciando maior magnetizao, em razo da presena de magnetita. Os valores de substituio isomrfica de Fe por Al variaram 0,07 a 0,11 e 0,09 a 0,38 mol mol-1 nas estruturas da hematita e magnetita, respectivamente.
Resumo:
Hidrxidos duplos lamelares (HDL) so intercaladores potenciais aninicos. Com o objetivo de obter fertilizantes de liberao lenta de nitrato, foram sintetizados HDL com a frmula geral [M2+1-xM3+x(OH)2]x-(NO3)x.yH2O, em que M2+ = Mg2+ e M3+ = Al3+ e, ou, Fe3+, utilizando-se o mtodo de coprecipitao a pH alcalino constante. Medidas de difrao de raios-X evidenciaram que a cristalinidade aumenta com o acrscimo do valor de pH e da razo molar M2+/M3+. As medidas de FTIR apresentaram bandas caractersticas de nitrato livre no espao interlamelar, alm de pequena contaminao de ons carbonato. Medidas de TGA/DTA possibilitaram a confirmao das composies e dos teores de ons de nitrato intercalados. As curvas de liberao de nitrato demonstraram dois comportamentos de liberao complementar, um inicial rpido (A) e um lento gradativo (D), sendo, este ltimo, relacionado orientao planar do on nitrato intercalado. Os materiais sintetizados e investigados neste trabalho apontaram grande potencial para serem utilizados como matrizes para fertilizantes de liberao lenta de nitrato.
Resumo:
Non crystalline (nc) EuIG and DyIG have been prepared by dcsputtering. Mssbauer data on 57Fe, 151Eu and 161Dy reveal sharp magnetic transitions at 62 K and 70 K for nc EuIG and DyIG, respectively. The 57Fe hyperfine (hf) spectra consist of three superpositioned patterns for Fe3+ in tetrahedral and octahedral and for Fe2+ in tetrahedral oxygen coordination. The saturation hf fields at 4.2 K are reduced compared to the values of the corresponding crystalline materials. The induced hf field at 151Eu is only 1/8 of that for crystalline EuIG
Resumo:
The distribution of Sn4+ cations within the five crystallographic sites of the magnetoplumbite (M) like compound BaFe122xCoxSnxO19 has been analyzed using singlecrystal xraydiffraction data. The species Fe3+ and Co2+ cannot be distinguished using x rays because of their very similar atomic numbers; however, the calculation of the apparent valencies for the different sites allows an insight into the Co2+ cation segregation. The use of previous data from neutron powder diffraction allows a precise picture of the cation distribution, which indicates a pronounced site selectivity for both Sn4+ and Co2+ cations. The Sn4+ cations prefer the 4f2 sites and to a much lower extent the 12k sites, while they do not enter the octahedral 2a sites at all. Co2+ cations are distributed among tetrahedral and octahedral sites displaying a clear preference for the tetrahedral 4f1 sites. Magnetic measurements indicate that the compound still exhibits uniaxial anisotropy with the easy direction parallel to the c axis. Nevertheless, the magnetic structure shows a considerable degree of noncolinearity. A strong reduction of the magnetic anisotropy regarding that of the undoped compound is also detected.
Resumo:
We report here on the magnetic properties of compounds of composition Fe1xCrxSbO4 and Fe1xGaxSbO4. The introduction of paramagnetic Cr3+ and diamagnetic Ga3+ into the rutilerelated iron antimonate lattice does not destroy the antisite atomic ordering which exists in iron antimonate of composition FeSbO4. The initial slope of the Curie temperature dependence on x is similar in both series, indicating that Fe3+Cr3+ interactions are very small. The magnetic susceptibility measurements recorded from the compounds of composition Fe1xCrxSbO4, x<0.4, and Fe0.9Ga0.1SbO4 show them to behave as spin glasses at low temperatures. The inhibition of compounds of the type Fe1xCrxSbO4, x>0.4, and Fe1xGaxSbO4, x>0.1 to undergo a spinglass transition above 4.2 K is associated with a dilution effect.
Hydrogen isotope fractionations between amphiboles, micas, and fluids in alkaline igneous intrusions
Resumo:
RSUM DE LA THSE Les teneurs des amphiboles en lments majeurs et en isotopes stables ont t analyses dans plusieurs complexes igns alcalins et hyperalcalins, dans le but de dterminer l'importance des variations de composition des minraux pour le fractionnement isotopique de l'hydrogne dans un systme naturel minral-magma-fluide. Cette tude se concentre principalement sur les synites nphliniques de complexes intrusifs alcalins bien connus mais chimie variable, dont les amphiboles, ainsi que d'autres silicates hydrats tels que micas et eudialytes, lorsque cela tait possible, ont t spars. L'intrt principal s'est port sur le complexe alcalin d'Ilmaussaq de la Province du Gardar, au Sud du Groenland. Dans une optique de comparaison, nous avons collect et analys d'autres chantillons provenant du complexe de Tugtutq (Sud Groenland), des complexes de Khibina et Lovozero (Pninsule de Kola, Russie), du Mont St-Hilaire et du Mont Royal (Canada) et de 6 autres du nord-ouest de la Namibie (Cape Cross, Okenyenya, Messum, Etaneno, Kalkfeld,et Okorusu). Les compositions isotopiques de l'hydrogne des amphiboles des ces diffrentes zones prsentent de grandes variations (-227 -700/00), ce qui est atypique pour des magmas d'origine mantellique. Les valeurs comprises entre -80 et -400/00 indiquent une provenance du manteau. Ces larges variations de compositions ainsi que l'extrme appauvrissement en isotope lourd de l'hydrogne (D), en comparaison avec d'autres roches ignes, semblent tre propres.aux roches alcalines et hyperalcalines de ce type, ce qui indiquerait un processus commun. Les diffrents complexes alcalins choisis prsentent un large intervalle de composition chimique des amphiboles. La caractrisation des amphiboles par microscopie lectronique et par spectroscopie Mssbauer contribuent observer le contrle du Fe sur le fractionnement des isotopes de l'hydrogne. En effet, cela a mis en vidence un contrle du Fe sur le fractionnement et mme, dans le cas du complexe hyperalcalin d'Ilmaussaq, une relation entre le rapport Fei3+/FeT et les variations du rapport D/H. Les complexes tudis diffrent de par leur index agpatique (Na+K/Al) et galement de par leur contenu en fer. Les plus hautes valeurs en Fe (27-35 wt%) et en lments alcalins dans les amphiboles, ainsi que les teneurs de D/H les plus basses et leur grande variation, sont celles du complexe d'Ilmaussaq. Les amphiboles de la Pninsule de Kola et du Canada sont similaires, mais toutefois moins appauvries en D. En ce qui concerne les amphiboles des complexes du NO de la Namibie, elles prsentent des compositions isotopiques de l'hydrogne magmatiques normales (-73 -100 0/00), contiennent moins de Fe (15-17 wt%) et sont fortement enrichies en Ca et moins en Na. Dans ce cas, l'alcalinit est moins importante en comparaison des autres complexes tudis. En dehors des teneurs en lments alcalins des amphiboles, l'alcalinit des fluides s'avre galement un facteur important, ce qui est cohrent avec certaines suggestions partir de systmes exprimentaux. Afin de mieux contraindre ce facteur, des expriences d'changes hydrothermaux entre les amphiboles et les fluides de salinit diffrente ont t effectues en simulant des conditions naturelles. L'approximation d'amphiboles naturelles de complexes igns alcalins, couple aux expriences d'change, aide prciser les facteurs contrlant le fractionnement des isotopes de l'hydrogne dans les roches alcalines. Les valeurs extrmement basses de 3D des amphiboles de ces complexes alcalins peuvent tre dues une combinaison de diffrents facteurs, telles qu'une haute alcalinit, une haute teneur en Fe et une faible profondeur d'intrusion. Les grandes variations ainsi que les faibles valeurs de SD des amphiboles tudies peuvent rsulter d'un processus magmatique interne et il est peu probable que de l'eau mtorique soit implique et/ou que le dgazage magmatique ait jou un rle. THESIS ABSTRACT Major element and stable isotope compositions of amphiboles were analyzed from a number of alkaline and peralkaline igneous complexes in order to determine the importance of compositional variations in minerals to hydrogen isotope fractionations in natural mineral-melt-fluid systems. The thesis mainly focuses on nepheline syenites of well-studied, but chemically variable alkaline intrusive rocks, from which amphiboles and, if possible, other hydrous silicates such as micas and eudialytes were separated. The system of primary interest was the alkaline Ilmaussaq Complex of the Gardar Province of South Greenland. For the purpose of comparison additional samples were collected and examined from the Tugtutq Complex (South Greenland), the Khibina and Lovozero Complexes (Kola Peninsular, Russia), Mount St-Hilaire and Mount Royal (Canada) and six further complexes from NW Namibia (Cape Cross, Okenyenya, Messum, Etaneno, Kalkfeld, and Okorusu). The hydrogen isotope compositions of amphiboles from the localities studied differ greatly, which is atypical for amphiboles from mantle, range between - 227 and - 700/00 (latter compatible with a simple mantle origin). As this wide range in compositions and the extreme depletion in the heavy hydrogen isotope (D) content relative to other igneous rocks appear to be unique to alkaline to peralkaline rocks of this type, a common process is indicated. The different alkaline complexes chosen cover a wide range of amphibole chemical compositions. Detailed chemical characterization of amphiboles by electron microprobe and Mssbauer spectroscopy analyses helped to constrain the control of Fe on the H-isotope fractionations. Complete characterization of the chemical compositions of the amphiboles support Fe-control on fractionations and at least for the peralkaline Ilmaussaq complex a relationship between Fe3+/FeT ratios and variations in D/H. The studied complexes differ in their agpaitic index (Na+K/Al) and also in their Fe-content. The most iron (27-35 wt. %) and alkaline element rich amphiboles, with the lowermost D/H ratio, as well with very wide range, are the ones from Ilmaussaq complex. Similar, but less D depleted amphiboles are from the Kola Peninsula and the Canadian localities. The complexes described from NW Namibia have amphiboles with normal magmatic hydrogen isotope composition (-730/00 to -1000/00), and have less Fe-content (15-17 wt. %), and are more Ca-and less Na-rich. In this case alkalinity is not that important in comparison to the other studied complexes. Beside the alkaline element contents in the amphiboles, the alkalinity of the fluids has been found to be an important factor, in conjunction with earlier suggestions from experimental systems. To further constrain this factor, hydrothermal exchange experiments between amphiboles and fluids of different salinity simulating natural conditions were performed. The approach of examining natural amphiboles from alkaline igneous complexes in parallel to performing exchange experiments - helped to further constrain the factors controlling the H-isotope fractionations in alkaline rocks. The observed changes between the hydrogen and oxygen isotope compositions of amphiboles and fluids before and after the experiments suggest that another phase was produced during the experiments, which influenced the final hydrogen isotope composition of the system. This presumably hydrous phase has also influenced the Fe3 +/Fe2+ ratio of the amphiboles, which became more oxidized. The extremely low SD values of amphiboles in these alkaline complexes may be due to a combination of different factors such as high alkalinity, high Fe-content, and shallow intrusion depths. This wide range and the low SD values of the amphiboles studied might be a result of internal, magmatic processes and it is unlikely that meteoric water was involved and/or magmatic degassing played an important role. RSUM DE LA THSE (pour le grand public) Fractionnement isotopique de l'hydrogne entre amphiboles, micas et fluides dans des intrusions alcalines Zsfia Wczek Directeur de thse, Prof. Torsten W. Vennemann Institut de Minralogie et Gochimie, Universit de Lausanne Les roches alcalines et celles qui leurs sont associes sont des sources importantes de nombreux minraux et minerais, tels l'apatite, le niobium, le diamant et autres pierres prcieuses. Cette tude se concentre sur des complexes alcalins localiss dans le sud du Groenland, au Canada, dans la pninsule de Kola en Russie et au nord-ouest de la Namibie. Ces complexes sont composs de roches ayant cristallis partir de magmas et de fluides trs enrichis en alcalins. Cet enrichissement permet la prcipitation de minraux inhabituels riches en potassium et/ou sodium, telles les amphiboles sodiques, galement enrichies en fer. Les amphiboles tudies ont des compositions calciques, sodi-calciques et sodiques, qui refltent leurs diffrents environnements de formation. Des tudes prcdentes ont rvl une large gamme de rapports isotopiques de l'hydrogne dans les amphiboles de roches hyperalcalines, dont certains extrmement bas. Cette variation importante est trs intrigante, sachant que des valeurs entre -40 et -800/00 correspondent des silicates igns hydrats et non altrs, alors que des valeurs descendant jusqu'a -1500/00 ncessiteraient une altration par de l'eau mtorique et/ou une contamination par les roches environnantes ou des sdiments riches en matire organique. Dans l cas prcis du complexe d'Ilmaussaq (sud du Groenland), aucune de ces explications n'a pu tre dmontre et des valeurs encore plus faibles ont t trouves. Le complexe d'Ilmaussaq prsente des valeurs de rapport isotopique de l'hydrogne entre -227 et -500/00 dans les amphiboles. Une origine mantellique permet d'expliquer les valeurs leves, mais d'autres processus doivent entrer en jeu pour engendrer les valeurs les plus ngatives. C'est l'identification de ces processus que nous nous sommes attachs dans ce travail. Les grandes variations observes dans les teneurs en fer et dans le rapport Fe3+/FeT des roches et des minraux de ces complexes sont corrles avec d'autres paramtres chimiques, tels que la composition isotopique de l'hydrogne dans les amphiboles. Nous avons ds lors abord les questions suivantes: quelle est la relation entre la teneur en fer des amphiboles et leur composition isotopique? Que nous apprennent les changements de la teneur en fer et les changements dans le rapport Fe3+/FeT sur les processus ptrologiques dans ces roches? Pour rpondre ces questions, nous avons analys les compositions isotopiques de l'oxygne et de l'hydrogne dans les amphiboles et d'autres silicates hydrats. La composition chimique et le rapport Fe3+/FeT des amphiboles ont galement t dtermins. Des expriences hydrothermales simulant des conditions naturelles ont t entreprises afin de mieux comprendre les processus de fractionnement isotopiques dans ces systmes trs alcalins. Nos conclusions sont les suivantes: (1) Les valeurs extrmement faibles ainsi que les larges variations des rapports isotopiques de l'hydrogne des amphiboles de ces complexes alcalins sont dues une combinaison de facteurs tels que la forte alcalinit, la haute teneur en fer et la profondeur trs faible de l'intrusion. (2) Ces valeurs sont probablement le rsultat de processus magmatiques internes. (3) Il est peu probable que les eaux mtoriques et/ou le dgazage magmatique aient jou un rle lors de la formation de ces amphiboles. (4) Certaines corrlations, en accord avec les tudes prcdentes, ont pu tre trouves au niveau des concentrations en fer. (5) Dans le cas du complexe d'Ilmaussaq exclusivement, une relation a t trouve entre le rapport Fe3+/FeT et la composition isotopique de l'hydrogne des amphiboles.
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Oxalic and oxamic acids are the ultimate and more persistent by-products of the degradation of N-aromatics by electrochemical advanced oxidation processes (EAOPs). In this paper, the kinetics and oxidative paths of these acids have been studied for several EAOPs using a boron-doped diamond (BDD) anode and a stainless steel or an air-diffusion cathode. Anodic oxidation (AO-BDD) in the presence of Fe2+ (AO-BDD-Fe2+) and under UVA irradiation (AO-BDD-Fe2+-UVA), along with electro-Fenton (EF-BDD), was tested. The oxidation of both acids and their iron complexes on BDD was clarified by cyclic voltammetry. AO-BDD allowed the overall mineralization of oxalic acid, but oxamic acid was removed much more slowly. Each acid underwent a similar decay in AO-BDD-Fe2+ and EFBDD, as expected if its iron complexes were not attacked by hydroxyl radicals in the bulk. The faster and total mineralization of both acids was achieved in AO-BDD-Fe2+-UVA due to the high photoactivity of their Fe(III) complexes that were continuously regenerated by oxidation of their Fe(II) complexes. Oxamic acid always released a larger proportion of NH4 + than NO3- ion, as well as volatile NOx species. Both acids were independently oxidized at the anode in AO-BDD, but in AO-BDD-Fe2+-UVA oxamic acid was more slowlydegraded as its content decreased, without significant effect on oxalic acid decay. The increase in current density enhanced the oxidation power of the latter method, with loss of efficiency. High Fe2+ contents inhibited the oxidation of Fe(II) complexes by the competitive oxidation of Fe2+ to Fe3+. Low current densities and Fe2+ contents are preferable to remove more efficiently these acids by the most potent AO-BDD-Fe2+-UVA method.
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Stable isotope compositions of a suite of magmatic amphiboles from alkaline basalts and andesitic rocks were examined to constrain the effects of degassing processes on the hydrogen isotope compositions. The Fe3+ (as Fe3+/Fe-total) and H2O contents, as well as the H isotope compositions of the amphiboles, differ markedly (27-58%, 0.5-2.2 wt%, -107 to -15 parts per thousand, respectively) but indicate systematic variations. The observed trends can be explained either as dehydrogenation or dehydration processes, both of which are coupled to oxidation processes, the latter most probably related to O2- substitution within amphiboles. The dehydrogenation-dehydration models can be used to assess the primary compositions of the magmas. As an important example, delta D values of amphiboles of Martian meteorites are discussed in a similar context. Copyright (c) 2006 John Wiley & Sons, Ltd.
Resumo:
Crystallisation of hydrous mafic magmas at high pressure is a subject of numerous petrologic and experimental studies since the last century and is mainly related to the process of continental crust formation and the possible link between mantle derived melts and low pressure granitoids. Albeit the sequence of crystallization is well constrained by experimental studies, the origin of exposed lower crustal rocks exposed on the earth surface is controversial. Ones line of argument is favouring high pressure crystallization of dry or wet mafic magmas, whereas others invoke partial melting of pre-existing crust. Therefore studies involving field, textural and chemical observations of exposed lower crust such as in Kohistan (Pakistan) or Talkeetna (Alaska) are crucial to understand the continental crust formation processes via arc magmatism. Epidote-bearing gabbros are very sparse and always associated with the deep part of continental crust (>30 km) as in the Kohistan Arc Complex (Pakistan) or in the Chelan Complex (western U.S.). Magmatic epidote is restricted to a small temperature interval above the water-saturated solidus of MORB and represent the last crystallizing liquids in lower crustal regions. However, epidote and melt stability at lower crustal pressures are not clearly established.The Chelan complex (western U.S.) at the base of the Cascadian Arc is composed mainly by peraluminous tonalit associated with gabbroic and ultramafic rocks and was traditionally interpreted as a migmatitic terrain. However field, chemical and mineralogical observations rather suggest a magmatic origin and point to a protracted crystallization at intermediate to high pressure ~ 1.0 GPa dominated by amphibole fractionation and followed by isobaric cooling down to 650C. Crystal fractionation modelling using whole rock composition and field constraints is able to generate peraluminous tonalit. The modelled crystallisation sequence and the volume proportions are in agreement with experimental studies performed at these pressures. The Chelan complex was thus not formed during a partial melting event, but represent the sequence of crystallisation occurring at the base of the crust. Massive fractionation of hornblende is able to generate peraluminous tonalit without significant assimilation of crustal rock.Similarly to the Chelan complex, the base of the Kohistan arc is composed of cumulates derived by high pressure crystallization of hydrous magma. In garnet gabbros, epidote occurs as magmatic phase, crystallising from hydrous interstitial melt trapped between grain boundaries at lower crustal pressures (Ρ ~ 1.2 GPa) for temperature of (650-700 C). Trace and REE signature in epidote indicate that epidote was formed through peritectic reaction involving garnet, clinopyroxene and plagioclase. At the beginning of the crystallisation epidote signature is dominated by REE content in the melt, whereas at the end the signature is dominated by reacting phases. Melt in equilibrium with epidote inferred from the partition coefficients available is similar to intrusive tonalit up the section indicating that hydrous melt was extracted from the garnet gabbros. In some gabbros epidote shows single homogeneous compositions, while in others coexisting epidote have different compositions indicating the presence of solvi along the Al-Fe3+ join. The overgowths are only observed in presence of paragonite in the assemblage, suggesting high water content. At high water content, the hydrous solidus is shift to lower temperature and probably intersects the solvi observed along the Al-Fe3+ join. Therefore, several compositions of epidote is stable at high water content.-La composition chimique de la crote continentale est considre comme similaire celle du magmatisme calco-alcalin de marge continentale active (enrichissement en lments mobiles dans les fluides, anomalies ngatives en Nb, Ta et lments haut potentiel lectronique, etc...). Cependant la nature andsitique de la crote continentale (Si02 > 60 wt%), rsultant des nombreuses intrusions de granitodes dans la crote suprieure, est sujette polmique et le lien entre les magmas drivs du manteau et les roches volues de faible profondeur n'est pas clairement tabli (fusion partielle de crote basaltique, cristallisation fractionne haute pression, etc...).Les affleurements de crote profonde sont rares mais prcieux, car ils permettent d'observer les phnomnes se passant grande profondeur. Le complexe de Chelan (Washington Cascades) en est un exemple. Form environ 30 km de profondeur, il est compos de roches gabbroques et ultramafiques, ainsi que de tonalits, qui furent souvent interprts comme le produit de la fusion partielle de la crote. Cependant, les relations de terrain, la chimie des lments majeurs et des lments traces sont cohrentes avec l'volution d'un complexe magmatique mafique dans la crote profonde ou moyenne ( 1.0 GPa), domine par le fractionnement de l'amphibole. Aprs son emplacement, le complexe a subi un refroidissement isobare jusqu' des tempratures de l'ordre de 650 C, dduit de la composition chimique des minraux. Un bilan de masse contraint pax les observations de terrain permet de calculer la squence et les volumes de fractionnement. Les facis volus lgrement hyperalumineux observs sur le terrain peuvent tre gnrs par la cristallisation de 3 % de websterite olivine, 12 % d'hornblendite pyroxne 33 % d'hornblendite, 19 % de gabbros, 15 % de diorite et 2 % de tonalit. Nous montrons ainsi qu'une srie de fractionnement contrle par l'amphibole permet de gnrer des tonalits sans assimilation de matriel crustal et l'exemple de Chelan illustre la viabilit de ce processus dans la formation de crote continentale.Les ractions proches du solidus satur en H20 dans les systmes basaltiques des pressions leves restent nigmatiques. Diverses expriences tendent montrer que l'pidote est stable dans ces conditions, mais rarement observe (dcrite ?) comme phase primaire dans les systmes naturels. Les pidotes trouves dans les gabbros de Jijal (nord-Pakistan) montrent des textures de type .magmatique telles qu'observes dans les roches volues. Le contenu en terres rares de ces pidotes est trs variable allant de signatures enrichies en terres rares lgres impliquant la prsence de liquide interstitiel des signatures compltement dprimes en ces mmes lments, voquant une cristallisation en coexistence avec du grenat. Ces diverses signatures refltent un chemin de cristallisation en prsence de liquide interstitiel et enregistrent des ractions pritectiques impliquant grenat, clinopyroxene et plagioclase des pressions de ~ 1.2 GPa pour des tempratures de 650-700 C. Cependant dans quelques chantillons deux ou trois compositions d'pidotes coexistent dmontrant la prsence de lacunes d'immiscibilit le long de la solution solide pidote-clinozosite. La forte teneur en H20 du liquide magmatique est certainement l'origine de la coexistence de deux compositions distinctes.
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In this study, (011)-highly oriented Sr, Nb co-doped BiFeO3 (BFO) thin films were successfully grown on SrRuO3/Si substrates by rf-magnetron sputtering. The presence of parasite magnetic phases was ruled out based on the high resolution x-ray diffraction data. BFO films exhibited a columnar-like grain growth with rms surface roughness values of 5.3 nm and average grain sizes of 65-70 nm for samples with different thicknesses. Remanent polarization values (2Pr) of 54 lC cm 2 at room temperature were found for the BFO films with a ferroelectric behavior characteristic of an asymmetric device structure. Analysis of the leakage mechanisms for this structure in negative bias suggests Schottky injection and a dominant Poole-Frenkel trap-limited conduction at room temperature. Oxygen vacancies and Fe3/Fe2 trap centers are consistent with the surface chemical bonding states analysis from x-ray photoelectron spectroscopy data. The (011)-BFO/ SrRuO3/Si film structure exhibits a strong magnetic interaction at the interface between the multiferroic film and the substrate layer where an enhanced ferromagnetic response at 5 K was observed. Zero-field cooled (ZFC) and field cooled (FC) magnetization curves of this film system revealed a possible spin glass behavior at spin freezing temperatures below 30 K depending on the BFO film thickness.
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The present paper is devoted to the results of experimental research undertaken into photocatalytical oxidation (PCO) of aqueous solutions of de-icing agents and aqueous extract of jet fuel. The report consists of introduction, literature review, description of materials and methods, discussion of results and conclusions. TiO2 was selected as a photocatalyst for the experiments with synthetic solutions of ethylene glycol, 2-ethoxyethanol and aqueous extract of jet fuel. To explain the PCO mechanisms affecting certain behaviour of de-icing agent under distinctive conditions, the following factors were studied: the impact of initial concentration of pollutant, the role of pH, the presence of tert-butanol as OH-radicals scavenger and mineral admixtures. PCO under solar radiation performed in two ways: catalysed by irradiated TiO2 slurry or by TiO2 attached to buoyant hollow glass micro-spheres. Special attention was paid to the energy-saving PCO with reduced intensity mixing of the slurry. The effect of PCO was assessed by determination of residual chemical oxygen demand of solution (COD) and by measuring of concentration of glycols. The PCO process efficiency was assumed to be dependent on the TiO2 suspension fractional composition. Thus, the following effects of solutions media were viewed: presence of organic admixtures, pH influence, mixing mode during the PCO. The effects of mineral admixtures - Ca2+, Fe3+/2+, Mn2+, SO42- - that are often present in natural and wastewater systems or produced during the degradation of organic pollutants and which can affect the rate of PCO of de-icing agents, were also investigated.
